Reproduction steps:
1. Click New Game
2. Click Cutom Game
3. Scroll down and select Empty World
4. Click start to start in creative
5. Place two Medium Cargo Containers side by side connecting the smaller ports.
6. Place one small reactor on cargo containers
7. Press Shift+F10 to spawn in 10 Steel Plates
8. Pick up Steel Plates
9. Place the plates into one of the Medium Cargo Containers
10. Try to move the Steel Plates from one Cargo Container to the other.(In this step the Steel Plates will not move)

Observed behavior:
I observed the Steel Plates will not move from one small block cargo container to another small block cargo container when using the smaller ports.

Expected behavior:
I expect the small ports on the Medium Cargo Container to transfer Steel Plates.